Systems and techniques for in-phase/quadrature estimation are described. As data frames are received at a wireless networking direct-conversion receiver, preambles of the data frames are examined to identify frequency-independent subcarriers. Preamble-based estimation is used to estimate in-phase/quadrature imbalance for frequency-independent subcarriers and blind estimation is used to estimate in-phase/quadrature imbalance for frequency-dependent subcarriers. The estimation may be performed continuously and refined as new frames are received. At appropriate intervals, compensation is performed using current imbalance estimates.
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1. An apparatus comprising: at least one processor; memory storing a program of instructions; wherein the memory storing the program of instructions is configured to, with the at least one processor, cause the apparatus to at least: receive one or more data frames transmitted to a direct conversion receiver operating in a wireless access network; examine a preamble of each data frame to determine whether the subcarrier transmitting the data frame exhibits linear independence; for each subcarrier exhibiting linear independence, perform preamble-based estimation to estimate in-phase/quadrature imbalance using frequency domain symbols appearing in the preamble; perform blind estimation to estimate the phase/quadrature imbalance of subcarriers that have not been determined to exhibit linear independence; generate an overall in-phase/quadrature imbalance estimate based on the preamble-based estimate and the blind estimation; and perform compensation based on the overall in-phase quadrature imbalance estimate.
A wireless receiver apparatus mitigates radio-frequency impairments by analyzing received data frames. The apparatus examines the preamble of each data frame received by a direct conversion receiver in a wireless network to identify subcarriers exhibiting linear independence. For linearly independent subcarriers, the apparatus uses the preamble to estimate in-phase/quadrature (I/Q) imbalance. For other subcarriers, it uses blind estimation to determine I/Q imbalance. An overall I/Q imbalance estimate is generated by combining these two estimation methods. Finally, the apparatus compensates for the estimated I/Q imbalance to improve signal quality.
2. The apparatus of claim 1 , wherein the preamble-based estimation is used to estimate phase error of local oscillator signals.
The wireless receiver apparatus described above uses preamble-based estimation to specifically estimate the phase error of local oscillator signals within the direct conversion receiver. This phase error estimation from the preamble data contributes to the overall in-phase/quadrature (I/Q) imbalance correction performed by the device. Analyzing the local oscillator phase enables a more accurate determination and compensation of I/Q imperfections.
3. The apparatus of claim 1 , wherein the overall in-phase/quadrature estimate is generated by averaging the phase error of local oscillator signals over multiple frames during periods in which channel and in-phase/quadrature imbalance parameters are invariant.
The wireless receiver apparatus described above generates the overall in-phase/quadrature (I/Q) estimate by averaging the phase error of local oscillator signals over multiple received data frames. This averaging is performed during periods where the communication channel characteristics and the I/Q imbalance parameters remain constant. Averaging across multiple frames improves the accuracy and robustness of the I/Q imbalance estimate by reducing the impact of noise and transient variations.
4. The apparatus of claim 1 , wherein the apparatus is further caused to collect statistics for received symbols, and wherein blind estimation comprises jointly using the collected statistics with the estimation of the phase mismatch of local oscillator symbols to estimate additional in-phase/quadrature imbalance parameters.
The wireless receiver apparatus described above collects statistics on received symbols. The blind estimation process combines these collected statistics with the estimation of the phase mismatch of local oscillator symbols to estimate additional in-phase/quadrature (I/Q) imbalance parameters. Jointly utilizing received symbol statistics during blind estimation allows for a more comprehensive and accurate characterization of I/Q impairments beyond local oscillator phase errors.
5. The apparatus of claim 1 , wherein the additional in-phase/quadrature imbalance parameters comprise at least one of: the estimated ratio of the composite gain on the quadrature branch over the in-phase branch on a specified subcarrier, wherein the composite gain is the product of the local oscillator signal and the gain of a low pass filter on a specified branch of a receiver; and phase mismatch of the low pass filters on different branches of the receiver.
The wireless receiver apparatus described above estimates additional in-phase/quadrature (I/Q) imbalance parameters. These parameters include the estimated ratio of the composite gain on the quadrature branch over the in-phase branch of a specified subcarrier. The composite gain is the product of the local oscillator signal and the gain of a low pass filter on that receiver branch. The parameters also include the phase mismatch of the low pass filters on different receiver branches. Quantifying these parameters allows the receiver to compensate for gain and phase errors occurring within the I/Q signal paths.
6. The apparatus of claim 1 , wherein the apparatus operates in a direct-conversion receiver operating under the IEEE 802.11 standard.
The wireless receiver apparatus described above operates as a direct-conversion receiver under the IEEE 802.11 wireless networking standard. The I/Q imbalance estimation and compensation techniques described are applied to devices implementing the 802.11 protocol to enhance their performance. This ensures improved communication and data reception in wireless network environments conforming to IEEE 802.11 specifications.
7. A method comprising: receiving one or more data frames transmitted to a direct conversion receiver operating in a wireless access network; examining a preamble of each data frame to determine whether the subcarrier transmitting the data frame exhibits linear independence; for each subcarrier exhibiting linear independence, performing preamble-based estimation to estimate in-phase/quadrature imbalance using frequency domain symbols appearing in the preamble; performing blind estimation to estimate the phase/quadrature imbalance of subcarriers that have not been determined to exhibit linear independence; generating an overall in-phase/quadrature imbalance estimate based on the preamble-based estimate and the blind estimation; and performing compensation based on the overall in-phase quadrature imbalance estimate.
A method for mitigating radio-frequency impairments in wireless communication involves receiving data frames by a direct conversion receiver in a wireless network. The preamble of each data frame is examined to determine if the subcarrier transmitting it shows linear independence. For linearly independent subcarriers, preamble-based estimation determines in-phase/quadrature (I/Q) imbalance using preamble frequency domain symbols. Blind estimation determines the phase/quadrature imbalance of other subcarriers. An overall I/Q imbalance estimate combines both estimation results, and compensation is performed to correct the I/Q imbalance, thereby improving signal quality.
8. The method of claim 7 , wherein the preamble-based estimation is used to estimate phase error of local oscillator signals.
The method for mitigating radio-frequency impairments described above uses preamble-based estimation to specifically estimate the phase error of local oscillator signals. This phase error estimation is then used to calculate the overall in-phase/quadrature (I/Q) imbalance, enabling I/Q correction. Analyzing the local oscillator phase enables a more accurate determination and compensation of I/Q imperfections.
9. The method of claim 7 , wherein the overall in-phase/quadrature estimate is generated by averaging the phase error of local oscillator signals over multiple frames during periods in which channel and in-phase/quadrature imbalance parameters are invariant.
The method for mitigating radio-frequency impairments described above generates the overall in-phase/quadrature (I/Q) estimate by averaging the phase error of local oscillator signals across multiple received data frames. This averaging is performed when the channel and I/Q imbalance parameters remain constant over time. Averaging across multiple frames improves the accuracy and robustness of the I/Q imbalance estimate by reducing noise and variations.
10. The method of claim 7 , further comprising collecting statistics for received symbols, and wherein blind estimation comprises jointly using the collected statistics with the estimation of the phase mismatch of local oscillator symbols to estimate additional in-phase/quadrature imbalance parameters.
The method for mitigating radio-frequency impairments described above includes collecting statistics for received symbols. Blind estimation jointly uses these statistics with the estimation of the phase mismatch of local oscillator symbols to estimate additional in-phase/quadrature (I/Q) imbalance parameters. This joint estimation approach improves the overall accuracy of I/Q imbalance parameter determination.
11. The method of claim 7 , wherein the additional in-phase/quadrature imbalance parameters comprise at least one of: the estimated ratio of the composite gain on the quadrature branch over the in-phase branch on a specified subcarrier, wherein the composite gain is the product of the local oscillator signal and the gain of a low pass filter on a specified branch of a receiver; and phase mismatch of the low pass filters on different branches of the receiver.
In the method for mitigating radio-frequency impairments described above, the additional in-phase/quadrature (I/Q) imbalance parameters that are estimated include the ratio of the composite gain on the quadrature branch over the in-phase branch for a subcarrier. The composite gain is the product of the local oscillator signal and the gain of a low pass filter. Another parameter estimated is the phase mismatch of the low pass filters on different receiver branches. Estimating these parameters allows a more precise I/Q correction.
12. The method of claim 7 , wherein the method is performed in a direct-conversion receiver operating under the IEEE 802.11 standard.
The method for mitigating radio-frequency impairments described above is performed in a direct-conversion receiver operating under the IEEE 802.11 standard. By applying this method in accordance with IEEE 802.11, I/Q imbalance estimation and correction can be achieved, and communication improved, in devices following this standard.
13. A non-transitory computer-readable medium storing a program of instructions execution of which by at least one processor configures an apparatus to at least: receive one or more data frames transmitted to a direct conversion receiver operating in a wireless access network; examine a preamble of each data frame to determine whether the subcarrier transmitting the data frame exhibits linear independence; perform preamble-based estimation to estimate in-phase/quadrature imbalance using frequency domain symbols appearing in the preamble; perform blind estimation to estimate the phase/quadrature imbalance of one or more linearly dependent and independent subcarriers; generate an overall in-phase/quadrature imbalance estimate based on the preamble-based estimate and the blind estimation; and perform compensation based on the overall in-phase quadrature imbalance estimate.
A non-transitory computer-readable medium stores instructions that, when executed, enable a device to mitigate radio-frequency impairments. The instructions cause the device to: receive data frames transmitted to a direct conversion receiver operating in a wireless network; examine each frame's preamble to see if its subcarrier exhibits linear independence; perform preamble-based estimation to estimate in-phase/quadrature (I/Q) imbalance for linearly independent subcarriers using frequency domain symbols; perform blind estimation to estimate I/Q imbalance for all subcarriers; generate an overall I/Q imbalance estimate from both methods; and compensate based on the I/Q imbalance estimate.
14. The non-transitory computer-readable medium of claim 13 , wherein the preamble-based estimation is used to estimate phase error of local oscillator signals.
The computer-readable medium described above, containing instructions for mitigating radio-frequency impairments, specifies that preamble-based estimation is used to estimate the phase error of local oscillator signals. This phase error estimate then becomes part of the overall in-phase/quadrature (I/Q) imbalance estimate, which drives the I/Q compensation process.
15. The non-transitory computer-readable medium of claim 13 , wherein the overall in-phase/quadrature estimate is generated by averaging the phase error of local oscillator signals over multiple frames during periods in which channel and in-phase/quadrature imbalance parameters are invariant.
The computer-readable medium described above, containing instructions for mitigating radio-frequency impairments, includes instructions to generate the overall in-phase/quadrature (I/Q) estimate by averaging the phase error of local oscillator signals across multiple received data frames. This averaging is done during periods when channel and I/Q imbalance parameters are stable. Averaging reduces noise and variations in the I/Q estimate.
16. The non-transitory computer-readable medium of claim 13 , wherein the apparatus is further configured to collect statistics for received symbols, and wherein blind estimation comprises jointly using the collected statistics with the estimation of the phase mismatch of local oscillator symbols to estimate additional in-phase/quadrature imbalance parameters.
The computer-readable medium described above, containing instructions for mitigating radio-frequency impairments, further configures the device to collect statistics for received symbols. The blind estimation process combines these statistics with the estimated phase mismatch of local oscillator symbols to estimate additional in-phase/quadrature (I/Q) imbalance parameters, thereby providing a more comprehensive estimation.
17. The non-transitory computer-readable medium of claim 13 , wherein the additional in-phase/quadrature imbalance parameters comprise at least one of: the estimated ratio of the composite gain on the quadrature branch over the in-phase branch on a specified subcarrier, wherein the composite gain is the product of the local oscillator signal and the gain of a low pass filter on a specified branch of a receiver; and phase mismatch of the low pass filters on different branches of the receiver.
The computer-readable medium described above, containing instructions for mitigating radio-frequency impairments, specifies that the additional in-phase/quadrature (I/Q) imbalance parameters include: the estimated ratio of the composite gain on the quadrature branch over the in-phase branch on a specified subcarrier, where the composite gain is the product of the local oscillator signal and the gain of a low pass filter; and phase mismatch of the low pass filters on different branches of the receiver.
18. The non-transitory computer-readable medium of claim 13 , wherein the apparatus operates in a direct-conversion receiver operating under the IEEE 802.11 standard.
The computer-readable medium described above, containing instructions for mitigating radio-frequency impairments, is used in a direct-conversion receiver operating under the IEEE 802.11 standard. This setup is aimed at improving the performance of IEEE 802.11-compliant devices by employing I/Q imbalance estimation and compensation techniques.
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March 31, 2015
July 4, 2017
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